


Project B.L.A.S.T.E.R

by CornucopiaOfMemes



Series: The Undertale Prank War [2]
Category: Undertale (Video Game)
Genre: Alphyne, Alphys - Freeform, Author Loves You, Chara and Gaster get along, Chara lowkey inlove with G, Dadster, Ecto-Penis (Undertale), Evil with a good reason, FLirting irting, Flirty Chara, Frans - Freeform, Fransoriel!, Frisk - Freeform, Gaster is le skeledaddy, Gaster/Chara - Freeform, Ghost Chara, Like thanos, Original Characters - Freeform, Papster - Freeform, Reader is You, Sans - Freeform, Sex, Shirtess, Smut, Soriel...?, Stripping, The Surface, Undyne - Freeform, What in detarmination is this fuckery, Yes im talking to you, You're oure in this story, as of saturday april second tgherr is no smut yet, but not really, but not...?, evil gaster, just no, maybe smut, noo way no how, not in a sexual way - Freeform, now theres smut, ok gonna write the story now bye, ok im too many tags, sorry bros, undertale on the surface, wait is masturbaton smut???, you Gaster
Language: English
Status: In-Progress
Published: 2020-04-02
Updated: 2020-04-12
Packaged: 2021-02-23 07:33:21
Rating: Not Rated
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 8
Words: 3,577
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/23441221
Author URL: https://archiveofourown.org/users/CornucopiaOfMemes/pseuds/CornucopiaOfMemes
Summary: (Takes place in the same AU as TGUPW, but after the prank war.)Gaster has been living with the monsters after a suspicipusly convenient meeting after the barrier was broken.He has been a good friend so far, but since his newest experiment started, he's been...different.talking to thin air...laughing at nothing...ever sleeping...it's been worrying Sans.
Series: The Undertale Prank War [2]
Series URL: https://archiveofourown.org/series/1684897
Comments: 1
Kudos: 5





	1. Gaster's Secret Project

"Entry number 1.

The experiment has been approved. this is monumental.  
The Void is a hard substance to control. i should know, i was trapped in there for five Decades.  
But with project B.L.A.S.T.E.R underway, it will be under my control forever.  
End Entry."  
With a sigh, Gaster ended his recording. he was glad it was approved, though he had lied to get the 'Power Core' ready to be expanded to the surface.  
Gaster had obviously already done.that. it was the first thing he'd ever sone as a scientist since coming back from the void.  
"Hey G." a voice said, interrupting his thoughts.  
"Yes Sans? What do you need?" He replied, turning to face his eldest son.   
Sans had changed his outfit since coming to the surface . His hoodie was a darker shade of blue, and he was wearing a black t-shirt underneath it with the desgn of a Gaster Blaster on it. His shorts stayed the same, but he actuallyg dedcided to put on shoes, and tie them too. his hood fuff was at 999% capacity, meaning it was extra fluffly.  
"Well, i just wanted to come in and say it's almost ten 'o clock. Paps already collapsed in his bed, the kid's gone along with Tori, Asgore, Alphys and Undyne." Gaster smiled. Everyone had happily integrated. Toriel had a bakery job, Asgore owned a gardening shop, Papyrus is papyrus, Alphys and Undyne are happily married, and Sans- "I'm only awake because i had a comedy show to host. I might have tickled a few FUNNY BONES." "Wow, that one MARROWly made it to the Good Pun Zone." He retorted. They both chucked before sans put out a hand.  
"C'mon, G. i know a shortcut home."


	2. Chapter 2: Insomni-Gaster

**Summary for the Chapter:**

> Gaster begins to lose sleep to his new obsession..

"Entry number two.

Project B.L.A.S.T.E.R., or Baritechnic Lethal Antimatter Stream for Trapping Eviscerating and Repurposing, is in its infant stage, as the first half of the lower jaw is now halway complete.  
end entry."

Gaster smiled. the project has started off wonderfully, he thinks to himself as he makes a cup of coffee. For some reason, Gaster was fond of working late into the night. Unfortunately, that means he woud be scolded by-  
"Sans, you can't sneak up on me." "And you can't survive without sleep. Gaster, come on."   
Since G had started to stay up late, Sans had been worried... but he didnt know why.  
"So, mind explaining what the hell that is?" Sans said, nodding towards the newly-begun jawbone "That, Sans, is Project B.L.A.S.T.E.R. In a nutshell, it uses the power of the void to... power things." Gaster could not reveal his scheme to Sans. it wouldn't make sense to the elder skeleton, and might kill him with it.  
"Uhh… yyyeeah, that sounds perfectly safe..." Sans said. he shook his head, and said,"Listen, G. it's twelve forty.you gotta head to bed..."   
Gaster chuckled, and replied with "I'll sleep tomorrow"  
"It's Already Tomorrow." Sans said, blue eye activated.  
"…It's not tomorrow... UNTIL I SLEEP." Gaster replied, Both eyes turning yellow.  
they stared each other down for a solid minute.  
"...If you're not coming home, I'm telling Papyrus what you did for a living back in the underground." Sans threatened.  
"If you tell that to Papyrus i'll tell him exactly who killed me." Gaster retorted, not backing down."  
"Fine. stay here, G. neglect your life and friends." Sans relented.  
"Have fun being alone, Dad." he said, shortcutting away.


	3. The Visitor

**Summary for the Chapter:**

> Two days after the incident with Sans, Gaster got visited by a ghost.   
> Sans is not happy.

"Entry number 3.  
The first jaw has been completed. I am not ready to test it, as it needs to be fully completed to function properly.

I had a visit from a ghost today. She introduced herself as Chara, and said she wanted to help me. She apparently has been stuck there before, and knows its ins and outs.  
End entry."  
Gaster chuckled darkly. His project was going wll. nobody knows about the blaster, but Sans was a problem.  
"Hey there, G~" A voice above him teased. He looked up to see his incorporeal companion floating above him, floating in a lazy position, winking as she reclined on nothing.  
"You recording your progress, i hear. it's clever." Chara noticed. she floated off her position and bent over to be face-to-face with Gaster. "Hello again,my friend. welcome back to the lab." he greeted, walking away to the complete half-jaw.   
"The blaster is coming along fast. almost nobody suspects of our plan." he turns to Chara and smiles. "And you've been a bigger help than you know." "And you've been a better companion than you know," She retorted, giggling. "I'm a lonely girl in the void~"   
Gaster's face flushed deep purple. "Oh really? And do you think of me whilst all alone in the infinite darness?" He said, approaching Chara. She giggled again and respondedc with, "Only some of you."  
He reached out to try and touch her face, but she turned t the door just as-  
Frisk walked in.  
"O-oh, Hello, child. what are you doing here?" he greeted them kindly, his blush leaving his face.  
They smiled, before signing, (Sans is a little sick today, so he told me to, 'Fetch the doc from his stupid lab for dinner.')  
"Wow.": Chara and Gaster said at the same time. then Gaster muttered "Jinx." before going to the control panels around the suspended half jaw. he presssed some buttons while Chara laughed. "You're really gonna go with them? Wow, and i thought you wanted to banish them to the void..." "I dont want to banish them exactly. now quiet down befored they notice." He muttered through clenched teeth.  
"Alright, Frisk. lets go." He said, walking with them.  
just before he left he saw Chara blow a kiss at him and wink.


	4. The Beginning of the End

**Summary for the Chapter:**

> Chara becomes a little more... 'open' to Gaster. But she's hiding something, He can tell.  
> A LOT OF 17+ or 18+ i forget im so sorry  
> :D  
> bfore i get to tghe memes.  
> if i misrepresented how you bootiiful ladies out there pleasur yourselves, i am so fucking sorry. im a boy who hasnt done it yet so i know nothing. if you feel like correctibg me, PLEASE do so. in the words of our lord and god Pewdiepie,   
> "We must respect Wamen"
> 
> ok memetime les go  
> Hope yalls having fun in quarantine  
> everything is cancelled  
> everything is gone cuz of covid-19  
> everything is canceeled  
> now we're stuuck in Quarantine
> 
> Corona ooh na na  
> half of the country's got corona ooh na na  
> the government just sent us home they learnin' yeah  
> half the country got corona  
> we conquered like the romans  
> oho oho ho no
> 
> my last made me feel like i would be alive again  
> but when i hugged you i felt somethin i never felt  
> don't come closer  
> dont wanna give you corona  
> i wont make you feel alright  
> stay six feet away from me
> 
> :D

"Entry number Four.

Chara has become a little bit of an issue.  
The last time she appeared today, she had no shirt on, only her bra, necklace, shorts and socks. To say the ultimate minimun, i was surprised, and she used that to her advantage.  
I need to get back to work.  
i am seriously behind schedule.  
End entry."

Gaster was pissed. His ghostly companion, Chara, had been very flirty these past few days. and he was having none of it. the next time she showed her face, he was going to-  
"-you were gonna what, exactly~?"  
...fuck.  
"Hello there, Chara. it would help me a lot if you did not try to court me into-" "-fucking my brains out? aww. and we were getting along so well!" She floated in front of him, and he realized how much trouble he was in.

Chara's outfit today DIDN'T EXIST.  
She chose to come visit Gaster completely nude... except for her necklace.

"...Chara, you... you can't be serious..." Chara smirked, playfully booping him on the nose (wait. nose hole? nostril? somone help whats the actual name for it? i will love you unconditionally if you tell me) and giggling. "Oh but i am. I think i deserve some thanks for helping out so much on your doomsday project~" Gaster was completely Skull-shocked. "Wh-!? Okay, first, it's not a doomsday device, second, what do you mean, your he-" Gaster was interrupted by Chara putting her hand over his mouth.  
to an observer, a hand just appeared out of nowhere and covered his mouth.  
"Oh, Gaster. You aren't suggesting i've been useless, are you?" before he could react, she continued. "Good. that's what i thought. Moving onto the... fun part~" Chara let go of his mouth and winked at him as he realized that a ghost just touched him.  
As he regained his wits, he heard a moan, and looked over to see his partner rubbing her clit and squeezing her own boobs, all while floating off the ground in front of Gaster.  
He turned around and tried his damn hardest to ignored the moaning and panting of Chara. He picked up his new addition to the project,half of a Gaster Blaster Skull.  
The piece of machinery was very stylish, 'cause you can't end an endless time loop that only served as an infinite nightmare to those who remembered it with just a white laser dragon skull. who does that anyway?  
Gaster's design for what he called 'The Eternity Decimator' was much better than the version Sans used, which to Sans and Papyrus' surprise, was meant to bypass the game's files- sorry, the 'SOUL Code' and set the damage dealt by the blaster to five damage, no invincibility frames- again, my bad, 'Post-Damage Invulnerability' no matter what the user's ATK stat was or is.  
Gaster smiled as he remembered the memories he had before falling into the void- Papyrus' child years, Sans learning what a pun is, and of course, (REDACTED), Gaster's gorgeous wife.

[Information not found. Skipping over corrupted* files...]

Gaster felt a few tears fall down his face as the memories flooded into his skull...  
Then immediately got flushed back down by the semi-intangible demon THOT behind him moaning and calling out his name as she rapidly thrusted three fingers inside her pussy, breathing heavily...  
"If she breathes..." he muttered, summoning a GB V2.1 next to himself, aimed at Chara and charged to the max.  
"Ah- G-gaster...!" she panted, arching her back as she orgasmed heavily, the feeling rushing through her body but no fluid actually emerging.  
"Talk to the blaster, child. Gaster's busy." He retorted, firing the blaster.  
"Wait, talk to the FU" she screamed, getting blasted backwards into the far wall, knocking her out instantly.  
"...good job." he said to the blaster, which growled happily and disappeared.  
"I think im losing it... i need to talk to my sons..." Gaster growled, walking out of his newly-impurified lab.

As he left, Chara smirked and laughed.  
"Gaster, you utter fool... you're so obsessed with your work and getting rid of me, you can't even see that I'm manipulating you for my own benefit."

"In this world, it's still kill or be killed!"  
"In this world, it's still kill or be killed!"

two insanity-induced laughs echoed into the void...


	5. The blaster is complete

**Summary for the Chapter:**

> Despite everything known to monsterkind trying to impede his progress, Gasters deviced was finished.

**Notes for the Chapter:**

> Its been about twelve weeks since the last chapter.

"Entry number 15.

Its done."

Gaster smiled. then chuckledd. then laughed. he couldnt stop laughing, just like Everyone couldnt leave him alone. he wasnt doing anything wrong, just erasing a small child with the power to reset entire universes.

see? nothing...

"Well well well, G. what have we here?" a voice said, and Gaster turned to see his so- no, his friend,Sans. "Yeah, dude. this seems really dangerous." Monster Kid said. Well, he wasnt exactly a kid anymore... everyone just called him Mike. he wwas ay taller now. taller than Undyne!   
"GASTER."  
Oh fuck.  
he snapped out of his insanity long enough to realize his mistakes when he saw Papyrus, an orange glow in his eye and wearing Sans' old jacket.  
"So... its come to this, huh?" Gaster chuckled, summoning six blasters around himself.  
"So be it. COME!" he roared, sending hundreds of bones out at the trio, blasters firing and bones piercing.  
in the chaos, G ran over to the control panel, delfected a bone and a laser beam into papyrus , and typed the code to activate the Blaster.  
"Youve already lost, Sans. its ready. and they aren't.  
BUT SHE IS!" he yelled as a familiar green-shirted brown-haired megalomaniac appeared out of nowhere with a knife, grabbed Sans, and shoved him through the wall and into the backyard.  
"GASTER! TURN AND FACE ME!" Papyrus shouted and readied to fight.  
"Okay." hed simply replied and six GB's flew towards Gaster's youngest son.


	6. Family No Longer Part I

**Summary for the Chapter:**

> Papyrus and Mike vs Gaster.  
> Sans vs Chara.  
> this can only end well.

"So, Papyrus, my son. it's come to this?"  
Gaster taunted Papyrus as he and Mike got ready to fight.  
"UNFORTUNATELY, YES. IM SORRY." he responded as he summoned a long bone and held it like a spear as Mike readied his new metallic arms.  
"Undyne's been anawful influence on you, Papyrus..." *Mike's ATK increased!* "Let me show you how to truly use a bone as a weapon." G said, summoning two bones spinning in front of his hands and twelve bones spinning around him like a saw.  
"Hm!" As papyrus charged G and mike fired off beams of magic,Gaster simply scoffed and hit his son with a wicked uppercut, followed by a quadruple combo by hitting him with the spinning bones into the air and spiking him into the ground with a collective of the bones.  
Papyrus hurt, but got back up and fired four bones at Gaster, who was dealing with Mike. He dodged three, but got caught on the shoulder by one, dropping his gaurd as Paps came in with a combo of his own  
Gaster got smashed into the wall by a thick bone, then booamerang'd back towards Papyrus, who had readied three blaster skulls and was about to fire, when G blinked out of tghe trap to smash his youngest son into the far wall, knocking him out.  
"Pff. Weakling . unworthy of being called my-" "Parry this you fucking casual!"  
W H A M!  
Mike ran in behind Gaster, left arm blazing with yellow magic, and smashed him into the wall by hitting him on the back with a magic boosted punch, then attemped to finish the doctor off with a laser from his mouth.  
When the smoke cleared, Gaster was gone.  
"Yes! I got him! now i gotta- fuck."  
That last part was due to seeing G about to K.O Mike with a kick to the head with the slight addition of Ten gaster blasters firing as Mike bpunced upward fom the hit, effectively knocking him out.

(Meanwhile...)

"Wow, you've gotten stronger sinces the last time we met... More than one HP!" Chara yelled up to Sans, who was standing on a Gaster Blaster.  
"yep. i figured id get in shape." he lazily replied, firing the blaster and landing a direct hit.  
"Wow. not even dodging...?"  
"Nah."  
"WHOA !" Sans said, jumping off the blaster and onto a new one. that was new. "Have you forgotten? you killed me. i got stuck in the void with the good doctor. when he got out , i came with him, but retained my ghostly form."  
Good to know, Sans thought as he fored eight bones at chara before smashing her with a GB skull. She got up as expected, and he activated his combo.  
As she jumpedd up to him, he grabbed her SOUL and flung her around, then grabbing a bone himself, smashed her into the ground, blasted her up, then repeated it twice more and finished it with a blaster to the side, sending Chara through the concrete walls and into the street, where she promptly got run over by a hotdog cart.  
"Phew. that was interesting. now lets help out paps and-" "Yes! I got him! now i gotta- Fuck!"  
Then Mike was sent hurtling through the wall and into the hills near the Lab.  
"Ugh. Watch out, G."


	7. Family No Longer

**Summary for the Chapter:**

> Sans vs Gaster.  
> Short chapter today. sorry!

"Hm. that 'mike' was rather powerful..." Gaster said after streching. He was a little tired, but it didnt really matter to him. he did what he had to do.  
"Hey G." A voice said from behind him. Gaster tensed himseld for the coming fight.  
He turned around and saw a very, very angvry Sans.  
"So we're just jumping to it, as per usual?" Gaster said, summoning two large hands and a blaster.  
For some reason, his vision flashed pink and saw a pink girl with spikes for arms, a creepy face and exploding pink hair. he shook it off and moved on.  
"You know it." Sans replied, summoning two blasters and an array of bones. his blue eye flashed pink for a second.  
"Very well." Gaster said, snapping his fingers and blasting sans with the giant blaster. as expected, Sans wasnt there anymore.  
"I know your tricks. You teleport away when I attack you to a different part of the building..." He raises his hands and the two hands disappear and the blaster move over him, making a protective shell.  
Sans had teleported to the roof of the lab, which had significant holes in it. He saw the blaster cover G, but could still hear him.  
"So, tell me, Sans. What happens..." a LOUD snap was heard.

Sans looked up and immediately started sweating.

"...if there's no spots left to hide?"

When Sans looked up and saw the biggest Gaster Blaster of his life, surrounded by six gigantic hands all charging upto vaproze the building.

[To Be Continued...]


	8. Family No Longer PT 2

**Summary for the Chapter:**

> Sans vs Gaster part two.

"Oh, shitshitshitshit..." Sans panted. he summoned as many Gaster blasters as his instincts allowed him to, which was about six.  
"Try and hide from this!" Gaster's voice rung out as one more Blaster was summoned. Sans knew he couldn't hide from that. He could delay it, though...  
He teleported to where G was hiding and aimed four bones at the skull of his protective blaster. "Surprise, G!" he said, slamming the bones into the skull, ripping it upward and destroying it.  
"Oh, hello, Sans. i didnt expect to see you here." Gaster said, aiming his own bones.  
"Well, too bad. im here. deal with it." Sans replied, winking. he readied his bones as they prepared to fight.  
Gaster scoffedd and his eyes flashed Red. The Two hands and the Gicantic blaster finished charging and fired their vrespective beams.  
both of Sans' eyes flashed blue with a black hole in the middle, makinghis blasters fire and counter the beam from the three above them.  
For a minute they seemed equally matched as they stared each other down.  
Then a hand grabbed Sans and threw him into the floor, and Gaster, bone in hand, knocked him up to the next floor and finished his combo with a punch from the big hand.  
"I wish it didnt have to be this way. Goodbye, Sans." Gaster said.  
"Yeah, me neither. Also Hi!" Sans said from behind him. G gasped and turned around only to be catapulted into a combo.  
Sans threw a ring of 20 bones around his body,and sent a few hundred bones toward Gaster. As he dodged them, Sans built up the speed of the bones around his body, and when G got to him, Sans jumped up, hitting him 10 times.  
Sans then threw two of them at him, effectively trapping Gaster for a second, but a second was all Sans needed to hurl the rest of his high-speed bones at him.  
Gaster managed to block most of the bones and put his right hand behinnd his back.   
"Honestly, Sans, you're the weakest of the family. I think both Mettaton and Papyrus lasted longer than you did. IIt's shame they both have to die..." He taunted the opposing skeleton. he was secretly praying Sans would take the bait.  
And he did.  
Momentarily forgetting about the Giganta Blaster and the H4ND5, He took most of his remaining magic and summoned exactly one metric fuck-ton of Blasters.  
"Oh." Was all Gaster managed to say before getting absolutely blasted out of the building and out into the hillside.   
A pile of bones boosted him right back to Sans, who aimed the Blasters at the floor where G landed.   
Instantly, his MASSIVE reservoir of HP dropped by 25%. [80,000 / 160K]   
He was tunneled into the ground for a solid minute. Gaster couldn't even see the sunlight.  
"Hey Sans! I think you're forgetting something!" G yelled up into the tunnl, before tapping a button on his wristwatch. Then he snapped his fingers.   
Sans heard the voice of his ex-father saying he forgot something when he heard a snap. he knew something bad was about to happen. "Wait. i forgot something...?" he mused.   
Then it clicked.  
"Gaster, you goddamn son of a B-" those were the only words Sans could manage before being utterly bathed in red energy. the entire building was getting vaporized around him. Control panels were torn up, Cameras and experiments were transformed to dust.   
Sans had barely enough HP to make it out of the blast, so he thought. When he tried to teleport out of there, he sighed in relief when he stopped feeling pain, then his eyes widened when he realized where he was.   
[Warning. you are unable to T.E.L.E.P.O.R.T. Doing so would result in system failure. Sending you back...]   
"Oh, come on, gimme a fuckin brea-"   
BOOM!   
When Gaster teleported to the surface, the entire lab was gone. all that remained...  
Was a blue jacket.  
Gaster's eyes flickered from Purple to Yellow.  
He gasped and ran over to the jacket. "Sans! Sans, no, no, fuck... Sans, No, dont…! Dont leave us! What will ido!? what will Papyrus do!? Sans, NOO!!" He screamed at the heavens.  
"Hmm... it seems the little G has devided to break out... bad idea..." A voice said from behind him.   
Gaster turned around to see... Chara, completely naked again.  
"You... you corrupted me..." He deduced, now thoroughly pissed. "You figured that out too late, mi amigo. now i think I'll just do this..." Chara responded, booping him on the nose. His eyes turned from yellow to purple.   
He was back to insanity.   
"Now, Gaster. i think i need your help. I have a scratch i just can't itch... think you can help me out~" She said, biting her lip and quivering her knees together.   
Gaster smirked and slaammed her down on an Adrenalume table that somehow survived the blast. His crotch started glowing a deep purple, and befored long, staeted to brutally fuck her.


End file.
